Some times their are blue and red peterbuilts in the game but they don't show up often.If you find one just follow it until it parks and then you can buy it.

A2:

To get a blue one start a new game from there go straght to mercury on the left hand side in murcury there is one you may not be able to aford it but click pause then type: wininalottery then click pause a gain this gives you more money and a license to hire